to be honest, I don't know exactly how the noise-reduction in a camera works.
I never use it, I try to avoid getting the noise in the first place.
I'm not too fond of using in-camera software like sharpening, noise-reduction etc.; too afraid that it damages the picture too much. Better to do it afterwards, then YOU are in control, not the camera.

If you still want to know, there are specialiced photographer-forums out there, better post the question there.

Like stefan said: try to avoid getting noise and if you have any noise do not use the camera software. Perhaps in 5 years there is that perfect tool to remove all noise without losing detail thats better than that was in your camera and then you still have you originals to de-noise